Feat: cse for gep incl. incomplete testing

[salinhkuhn]

This PR adds GEP to the CSE pass. In the output of #886 I noticed that a series of identical GEPs appear namely the same getelementptr (same base, index, elem_type, and noWrapFlags) recomputed many times within a single basic block. The change routes adds getelementptr to the existing Veir/Passes/CSE.lean. GEP is pure pointer arithmetic (afaiu, https://llvm.org/docs/GetElementPtr.html).

Testing still incomplete:

• need to add the file check

[github-actions]

VeIR Benchmarks

Details

Benchmark suite	Current: 5de1119	Previous: 936c95c	Ratio
add-fold-worklist/create	1083000 ns (± 22808)	2348000 ns (± 97457)	0.46
add-fold-worklist/rewrite	2023000 ns (± 34825)	4141000 ns (± 38823)	0.49
add-fold-worklist-local/create	1108000 ns (± 16906)	2291000 ns (± 44019)	0.48
add-fold-worklist-local/rewrite	1783000 ns (± 26013)	3404000 ns (± 88004)	0.52
add-zero-worklist/create	1128000 ns (± 56839)	2372500 ns (± 138531)	0.48
add-zero-worklist/rewrite	1319000 ns (± 30762)	2552000 ns (± 62280)	0.52
add-zero-reuse-worklist/create	936000 ns (± 21260)	2026500 ns (± 127621)	0.46
add-zero-reuse-worklist/rewrite	1073000 ns (± 19204)	2122000 ns (± 69455)	0.51
mul-two-worklist/create	1109000 ns (± 23900)	2292000 ns (± 111491)	0.48
mul-two-worklist/rewrite	2844000 ns (± 62219)	5580000 ns (± 86102)	0.51
add-fold-forwards/create	1086000 ns (± 91972)	2422000 ns (± 118219)	0.45
add-fold-forwards/rewrite	1577500 ns (± 514693)	2986000 ns (± 45152)	0.53
add-zero-forwards/create	1084000 ns (± 18152)	2488000 ns (± 113288)	0.44
add-zero-forwards/rewrite	982000 ns (± 31230)	1997000 ns (± 35374)	0.49
add-zero-reuse-forwards/create	931000 ns (± 3564)	1865000 ns (± 10756)	0.50
add-zero-reuse-forwards/rewrite	798000 ns (± 9762)	1537000 ns (± 16432)	0.52
mul-two-forwards/create	1088000 ns (± 16239)	2287000 ns (± 42759)	0.48
mul-two-forwards/rewrite	1837000 ns (± 37785)	3584000 ns (± 30971)	0.51
add-zero-reuse-first/create	904000 ns (± 24224)	1983000 ns (± 107910)	0.46
add-zero-reuse-first/rewrite	9000 ns (± 447)	8000 ns (± 1840)	1.13
add-zero-lots-of-reuse-first/create	909000 ns (± 17978)	1920500 ns (± 103233)	0.47
add-zero-lots-of-reuse-first/rewrite	415000 ns (± 5983)	776000 ns (± 30418)	0.53

This comment was automatically generated by workflow using github-action-benchmark.

[regehr]

thanks Sarah! I believe this change is correct, but please add a test case showing that it works and maybe also one showing that it does not merge a gep inbounds with a regular gep

also note that this version of CSE is pretty weak, it does not work across basic blocks-- there's a problem with the dominator analaysis that needs to be fixed before this is a somewhat useful CSE pass

[tobiasgrosser]

@salinhkuhn, is this now ready for review?